/**
 * Copyright (C) 2002-2015   The FreeCol Team
 * <p>
 * This file is part of FreeCol.
 * <p>
 * FreeCol is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 * <p>
 * FreeCol is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.server.ai.mission;

import java.util.List;
import java.util.logging.Logger;

import javax.xml.stream.XMLStreamException;

import net.sf.freecol.common.io.FreeColXMLReader;
import net.sf.freecol.common.io.FreeColXMLWriter;
import net.sf.freecol.common.model.Colony;
import net.sf.freecol.common.model.Europe;
import net.sf.freecol.common.model.Location;
import net.sf.freecol.common.model.PathNode;
import net.sf.freecol.common.model.Player;
import net.sf.freecol.common.model.Unit;
import net.sf.freecol.common.model.pathfinding.CostDecider;
import net.sf.freecol.common.model.pathfinding.CostDeciders;
import net.sf.freecol.common.model.pathfinding.GoalDecider;
import net.sf.freecol.common.model.pathfinding.GoalDeciders;
import net.sf.freecol.common.util.LogBuilder;
import net.sf.freecol.server.ai.AIMain;
import net.sf.freecol.server.ai.AIMessage;
import net.sf.freecol.server.ai.AIUnit;


/**
 * Mission for cashing in a treasure train.
 * FIXME: acquire protection
 * FIXME: Better avoidance of enemy units
 */
public class CashInTreasureTrainMission extends Mission
{

    private static final Logger logger = Logger.getLogger( CashInTreasureTrainMission.class.getName( ) );

    /** The tag for this mission. */
    private static final String tag = "AI treasureTrain";

    /**
     * The location to cash this treasure train in at, either a Colony
     * or Europe.
     */
    private Location target;


    /**
     * Creates a mission for the given <code>AIUnit</code>.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param target The target <code>Location</code> for this mission.
     */
    public CashInTreasureTrainMission( AIMain aiMain, AIUnit aiUnit,
                                       Location target )
    {
        super( aiMain, aiUnit, target );
    }

    /**
     * Creates a new <code>CashInTreasureTrainMission</code> and reads
     * the given element.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param xr The input stream containing the XML.
     * @throws XMLStreamException if a problem was encountered
     *      during parsing.
     * @see net.sf.freecol.server.ai.AIObject#readFromXML
     */
    public CashInTreasureTrainMission( AIMain aiMain, AIUnit aiUnit,
                                       FreeColXMLReader xr ) throws XMLStreamException
    {
        super( aiMain, aiUnit );

        readFromXML( xr );
    }

    /**
     * Assign a carrier for this treasure.
     *
     * @param lb A <code>LogBuilder</code> to log to.
     * @return A suitable carrier <code>AIUnit</code>, to which this unit
     *     has been queued for transport.
     */
    private AIUnit assignCarrier( LogBuilder lb )
    {
        final AIUnit aiUnit = getAIUnit( );
        final Unit unit = getUnit( );
        final Player player = unit.getOwner( );
        final Europe europe = player.getEurope( );

        List< Unit > carriers = player.getCarriersForUnit( unit );
        if ( carriers.isEmpty( ) ) return null;

        // Pick the closest carrier and queue this unit.
        final Location here = unit.getLocation( );
        int turns = Unit.MANY_TURNS;
        Unit closest = null;
        for ( Unit c : carriers )
        {
            int t = c.getTurnsToReach( here );
            if ( turns > t )
            {
                turns = t;
                closest = c;
            }
        }
        final AIMain aiMain = getAIMain( );
        TransportMission tm;
        AIUnit aiCarrier;
        if ( closest != null
                && ( aiCarrier = aiMain.getAIUnit( closest ) ) != null
                && ( tm = aiCarrier.getMission( TransportMission.class ) ) != null )
        {
            setTarget( europe );
            aiUnit.changeTransport( aiCarrier );
            if ( tm.forceCollection( aiUnit, lb ) )
            {
                lb.add( " forced collection on ", aiCarrier.getUnit( ) );
                return aiCarrier;
            }
        }
        return null;
    }

    /**
     * Extract a valid target for this mission from a path.
     *
     * @param aiUnit A <code>AIUnit</code> to perform the mission.
     * @param path A <code>PathNode</code> to extract a target from,
     *     (uses the unit location if null).
     * @return A target for this mission, or null if none found.
     */
    public static Location extractTarget( AIUnit aiUnit, PathNode path )
    {
        if ( path == null ) return null;
        final Location loc = path.getLastNode( ).getLocation( );
        Colony colony = loc.getColony( );
        return ( loc instanceof Europe
                && invalidReason( aiUnit, loc ) == null ) ? loc
                : ( colony != null
                && invalidReason( aiUnit, colony ) == null ) ? colony
                : null;
    }

    /**
     * Evaluate a potential cashin mission for a given unit and
     * path.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path A <code>PathNode</code> to take to the target.
     * @return A score for the proposed mission.
     */
    public static int scorePath( AIUnit aiUnit, PathNode path )
    {
        Location loc;
        if ( path == null
                || ( loc = extractTarget( aiUnit, path ) ) == null
                || ( loc instanceof Colony
                && invalidFullColonyReason( aiUnit, loc.getColony( ) ) != null ) )
        { return Integer.MIN_VALUE; }
        return aiUnit.getUnit( ).getTreasureAmount( ) / ( path.getTotalTurns( ) + 1 );
    }

    /**
     * Makes a goal decider that checks cash in sites.
     *
     * @param aiUnit The <code>AIUnit</code> to search with.
     * @param deferOK Keep track of the nearest colonies to use as a
     *     fallback destination.
     * @return A suitable <code>GoalDecider</code>.
     */
    private static GoalDecider getGoalDecider( final AIUnit aiUnit,
                                               final boolean deferOK )
    {
        GoalDecider gd = new GoalDecider( )
        {
            private PathNode bestPath = null;
            private int bestValue = Integer.MIN_VALUE;

            @Override
            public PathNode getGoal( ) { return bestPath; }

            @Override
            public boolean hasSubGoals( ) { return true; }

            @Override
            public boolean check( Unit u, PathNode path )
            {
                Location loc = extractTarget( aiUnit, path );
                if ( ( loc instanceof Colony
                        && invalidFullColonyReason( aiUnit, ( Colony ) loc )
                        == null )
                        || loc instanceof Europe )
                {
                    int value = scorePath( aiUnit, path );
                    if ( bestValue < value )
                    {
                        bestValue = value;
                        bestPath = path;
                        return true;
                    }
                }
                return false;
            }
        };
        return ( deferOK ) ? GoalDeciders.getComposedGoalDecider( false, gd,
                                                                  GoalDeciders.getOurClosestSettlementGoalDecider( ) )
                : gd;
    }

    /**
     * Find a suitable cash in location for this unit.
     *
     * @param aiUnit The <code>AIUnit</code> to execute this mission.
     * @param range The maximum number of moves to search.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A <code>PathNode</code> to the target, or null if not found
     *     which includes the case when Europe should be preferred (because
     *     the unit can not get there by itself).
     */
    private static PathNode findTargetPath( AIUnit aiUnit, int range,
                                            boolean deferOK )
    {
        if ( invalidAIUnitReason( aiUnit ) != null ) return null;
        final Unit unit = aiUnit.getUnit( );
        final Location start = unit.getPathStartLocation( );
        final Player player = unit.getOwner( );
        final Europe europe = player.getEurope( );
        final Unit carrier = unit.getCarrier( );
        final CostDecider standardCd
                = CostDeciders.avoidSettlementsAndBlockingUnits( );
        PathNode path;

        if ( player.getNumberOfSettlements( ) <= 0 || start == null )
        {
            // No settlements or not on the map, so go straight to
            // Europe.  If Europe does not exist then this mission is
            // doomed.
            return ( europe == null ) ? null
                    : unit.findPath( unit.getLocation( ), europe, carrier,
                                     standardCd );
        }

        // Can the unit get to a cash in site?
        return unit.search( start, getGoalDecider( aiUnit, deferOK ),
                            standardCd, range, carrier );
    }

    /**
     * Finds a suitable cashin target for the supplied unit.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param range The maximum number of moves to search.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A <code>PathNode</code> to the target, or null if none found.
     */
    public static Location findTarget( AIUnit aiUnit, int range,
                                       boolean deferOK )
    {
        PathNode path = findTargetPath( aiUnit, range, deferOK );
        return ( path != null ) ? extractTarget( aiUnit, path )
                : Location.upLoc( findCircleTarget( aiUnit,
                                                    getGoalDecider( aiUnit, deferOK ), range * 3, deferOK ) );
    }

    /**
     * Why would this mission be invalid with the given unit?
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @return A reason why the mission would be invalid with the unit,
     *     or null if none found.
     */
    private static String invalidMissionReason( AIUnit aiUnit )
    {
        String reason = invalidAIUnitReason( aiUnit );
        if ( reason != null ) return reason;
        final Unit unit = aiUnit.getUnit( );
        return ( ! unit.canCarryTreasure( ) ) ? "unit-cannot-carry-treasure"
                : ( unit.getTreasureAmount( ) <= 0 ) ? "unit-treasure-nonpositive"
                : null;
    }

    /**
     * Why is this mission invalid with a given colony target, given that
     * intermediate colonies are excluded.
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param colony The potential target <code>Colony</code>.
     * @return A reason for mission invalidity, or null if none found.
     */
    private static String invalidFullColonyReason( AIUnit aiUnit,
                                                   Colony colony )
    {
        String reason = invalidTargetReason( colony,
                                             aiUnit.getUnit( ).getOwner( ) );
        return ( reason != null )
                ? reason
                : ( ! aiUnit.getUnit( ).canCashInTreasureTrain( colony.getTile( ) ) )
                ? "cashin-impossible-at-location"
                : null;
    }

    /**
     * Why is this mission invalid with a given colony target, given that
     * intermediate colonies are included.
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param colony The potential target <code>Colony</code>.
     * @return A reason for mission invalidity, or null if none found.
     */
    private static String invalidColonyReason( AIUnit aiUnit, Colony colony )
    {
        return invalidTargetReason( colony, aiUnit.getUnit( ).getOwner( ) );
    }

    /**
     * Why is this mission invalid with a given Europe target?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param europe The potential target <code>Europe</code>.
     * @return A reason for mission invalidity, or null if none found.
     */
    private static String invalidEuropeReason( AIUnit aiUnit, Europe europe )
    {
        return invalidTargetReason( europe, aiUnit.getUnit( ).getOwner( ) );
    }

    /**
     * Why would this mission be invalid with the given AI unit and location?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param loc The <code>Location</code> to check.
     * @return A reason for invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit, Location loc )
    {
        String reason = invalidMissionReason( aiUnit );
        return ( reason != null )
                ? reason
                : ( loc instanceof Colony )
                ? invalidColonyReason( aiUnit, ( Colony ) loc )
                : ( loc instanceof Europe )
                ? invalidEuropeReason( aiUnit, ( Europe ) loc )
                : Mission.TARGETINVALID;
    }

    /**
     * Why would this mission be invalid with the given AI unit?
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @return A reason for invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit )
    {
        return invalidMissionReason( aiUnit );
    }


    // Implement Mission
    //   Inherit dispose, getTransportDestination, isOneTime

    /**
     * {@inheritDoc}
     */
    @Override
    public int getBaseTransportPriority( )
    {
        return getUnit( ).getTreasureAmount( );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTarget( )
    {
        return target;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setTarget( Location target )
    {
        if ( target == null
                || target instanceof Europe || target instanceof Colony )
        {
            this.target = target;
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location findTarget( )
    {
        return findTarget( getAIUnit( ), 20, true );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String invalidReason( )
    {
        return invalidReason( getAIUnit( ), target );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Mission doMission( LogBuilder lb )
    {
        lb.add( tag );
        String reason = invalidReason( );
        if ( isTargetReason( reason ) )
        {
            return retargetMission( reason, lb );
        }
        else if ( reason != null )
        {
            return lbFail( lb, false, reason );
        }

        for ( ; ; )
        {
            // Go to the target.
            final Unit unit = getUnit( );
            Unit.MoveType mt = travelToTarget( getTarget( ),
                                               CostDeciders.avoidSettlementsAndBlockingUnits( ), lb );
            switch ( mt )
            {
                case MOVE: // Arrived
                    break;

                case MOVE_HIGH_SEAS:
                case MOVE_NO_MOVES:
                case MOVE_NO_REPAIR:
                case MOVE_ILLEGAL:
                    return lbWait( lb );

                case MOVE_NO_ACCESS_EMBARK:
                case MOVE_NO_TILE:
                    return this;

                default:
                    return lbMove( lb, mt );
            }

            // Cash in now if:
            // - already in Europe
            // - or can never get there
            // - it is free to transport the treasure
            // - or there is no potential carrier to get the treasure to there
            // Otherwise, it is better to send to Europe.
            lbAt( lb );
            final AIUnit aiUnit = getAIUnit( );
            final Europe europe = getUnit( ).getOwner( ).getEurope( );
            if ( unit.canCashInTreasureTrain( ) )
            {
                AIUnit aiCarrier = null;
                boolean cashin = unit.isInEurope( )
                        || europe == null
                        || unit.getTransportFee( ) == 0;
                if ( ! cashin && aiUnit.getTransport( ) == null )
                {
                    cashin = assignCarrier( lb ) == null;
                }
                if ( cashin )
                {
                    return ( AIMessage.askCashInTreasureTrain( aiUnit ) )
                            ? lbDone( lb, false, "cashed in" )
                            : lbFail( lb, false, "cashin" );
                }
            }
            return retargetMission( "transport expected", lb );
        }
    }


    // Serialization

    private static final String TARGET_TAG = "target";


    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeAttributes( FreeColXMLWriter xw ) throws XMLStreamException
    {
        super.writeAttributes( xw );

        if ( target != null )
        {
            xw.writeAttribute( TARGET_TAG, target.getId( ) );
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readAttributes( FreeColXMLReader xr ) throws XMLStreamException
    {
        super.readAttributes( xr );

        target = xr.getLocationAttribute( getGame( ), TARGET_TAG, false );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String getXMLTagName( ) { return getXMLElementTagName( ); }

    /**
     * Gets the tag name of the root element representing this object.
     *
     * @return "cashInTreasureTrainMission".
     */
    public static String getXMLElementTagName( )
    {
        return "cashInTreasureTrainMission";
    }
}
